When Ralph wanders down to the ocean on the side of the island that they do not normally spend time on, the ocean seems to stretch on forever, as though the horizon is somehow farther away on that side. The enormity of it overwhelms Ralph and makes him feel that rescue is absolutely impossible.
Whereas on the other side of the island, the boys often see mirages in the simmering heat and think that there are other islands close by or sometimes even ships that might see their signal fire and come to rescue them. It would appear that Ralph's hopes are somewhat irrational on one side of the island and somehow more rational on the other.
Ralph, Jack and a number of the other boys had ventured to the other side of the island in search of the beast. They were taking a break and Ralph had an opportunity to peruse the environment.
Ralph was overwhelmed by the power of the ocean. It looked menacing and savage. The deep sea waves were enormous and seemed to serve an unknown purpose. It was as if the waves disregarded the island and seemed to want to overwhelm it with its power. The text describes the sea as if it were an animal, a predator: 'pausing, gather and rise with a roar.' It ascended the outcrops and points and finally touched him with its spray. The personification creates an image of someone vicious trying to reach him.
In contrast, the other side of the island was much calmer. Ralph thought of 'the quiet lagoon.' It was the place where they could build shelters and feel somewhat at home. On that side they could hope for rescue and could see mirages. The current was much calmer there and no one feared the ocean. There was a beach as well, which made it accommodating and gave them opportunity to relax and indulge in little pleasures. There they felt free.
On the side at which they were, however, the sea was so much rougher and aggressive. There were only rocks, which made the area seem even more alien and challenging. What impressed Ralph the most, though, was the sheer enormity of the ocean. Its size made it seem as if rescue was impossible since it seemed so remote. Ralph felt isolated and numb. He realized that that part of the island symbolized their removal from civilization. It was the barrier that separated them from the rest of the world. In that instant he felt trapped, helpless and condemned.
Simon comforted him and told him,
“You’ll get back to where you came from.”
In saying that, Simon ironically foreshadowed his own demise and Ralph's survival and eventual rescue.
The answer wrapped up into a nutshell is that the new side of the island deteriorates Ralf's hopes of being rescued. The other side gave him hope but this side shows the enormity of the ocean and makes him feel isolated.